The present invention relates to an-embedded signalling system and more particularly, to a system for embedding a code signal in an audio signal in a manner such that the composite signal is not readily distinguishable from the original audio signal by listening and in a manner such that the code signal cannot be readily removed or obscured without simultaneously degrading the quality of the audio signal.
There are numerous reasons for providing a system or means for readily identifying the source of an audio signal. In the music and recording industries in particular, such a system is desired
for automatic broadcast performance accounting and auditing of air play to assist with market planning PA0 for auditing released product from licensed tracks to confirm their source PA0 for administrative control of music tracks in studio and manufacturing operations PA0 for determining the source of unauthorized master release for auditing electronic delivery channels to establish proper royalty payment PA0 for proof of original track where a sound-alike is claimed PA0 for detecting sampled music tracks which are incorporated in new sound recordings PA0 for controlling authorization to copy PA0 for identifying copyright infringement by direct copying and PA0 for automatically cataloging the contents of an audio library.
As will be understood, it is highly desirable that the identifying information utilized by such a system not be easily deleted or obscured, e.g., by the adding in of additional audio material or by the re-recording of the material onto a different media. Systems that rely on a proprietary adaptation of the digital format used for recording audio signals in various high quality media such as compact discs and digital audio tape (DAT) are subject to such problems since once the original digital recording is converted to analog form, the identifying information is typically lost or no longer recoverable.
While it is thus desirable that the identifying information be permanently and inseparably intertwined with the original audio signal, it is also important that the presence of the code signal representing this information not interfere with the usual intended use of the audio signal, e.g., by not degrading the quality of an audio signal intended for entertainment.
Among the several objects in the present invention, it may be noted the provision of a novel method for embedding code symbols in an audio signal; the provision of such a method which results in a composite audio signal which is not readily distinguishable from the original by listening; the provision of such a method in which the composite audio signal is not readily modifiable so as to obscure or eliminate the code symbols without simultaneously degrading the quality of the audio signal; the provision of such a method in which the code symbols may be reliably extracted from the composite audio signal and the provision of such a method which may be implemented relatively simply and inexpensively. Other objects and features will be in part apparent and in part pointed out hereinafter.